This invention relates to a process for removing nitrosating agents from 1-chloro-2,6-dinitro-4-(trifluoromethyl)benzene, from which it is possible to obtain technical TRIFLURALIN with a particularly low nitrosoamine content (specifically NDPA).
It is well known that certain agricultural products can contain nitrosoamines, and the danger of these substances is equally well known.
In particular, it has been public knowledge since 1976 that nitrosoamines are present in formulations of agricultural products such as TRIFLURALIN ##STR1## which is a very important selective herbicide, and is prepared by the following reaction ##STR2##
This compound contains N-nitrosodipropylamine (NDPA), i.e. (CH.sub.3 CH.sub.2 CH.sub.2).sub.2 N--NO as impurity, this forming during the herbicide synthesis.
This is because 1-chloro-2,6-dinitro-4-(trifluoromethyl)benzene (DINITRO-PCBT), which is prepared by dinitrating 1-chloro-4-(trifluoromethyl)benzene (PCBT), and which is the starting substance for synthesising TRIFLURALIN, contains dissolved nitrogen oxides of various composition, which are responsible for the formation of nitrosoamines in accordance with the reaction (CH.sub.3 CH.sub.2 CH.sub.2).sub.2 NH+(NO).sub.x .fwdarw.(CH.sub.3 CH.sub.2 CH.sub.2)N--NO which takes place in a basic environment.
As stated, the danger of nitrosoamines is well known. They exercise an acute hepatotoxic action, and in particular are carcinogenic, mutagenic and teratogenic. It is therefore essential that the quantity of NDPA in the TRIFLURALIN is as low as possible, and legislation in the more advanced countries considers that an NDPA content in the technical product of less than 1 ppm is acceptable.
From research carried out up to the present time, it has emerged that if the DINITRO-PCBT is synthesised without special purification processes, the quantity of dissolved nitrogen oxides is such as to generate an NDPA content of between 150 and 500 ppm in the technical TRIFLURALIN subsequently produced. If purification processes are introduced (for example those indicated in U.S. Pat. No. 4,120,905), the nitrosating agents contained in the DINITRO-PCBT are reduced, but the results obtained are not constant and it is not possible to obtain technical TRIFLURALIN with an NDPA content of less than 1 ppm.
Research has therefore been directed towards methods which provide for eliminating the formed nitrosoamines from the final product.
Even if they allow a final product of satisfactory characteristics to be obtained, processes which comprise the destruction of preformed nitrosoamines have the very serious drawback of being dangerous because of the presence of nitrosoamines in certain stages of the process during which contact, including accidental contact, is always possible with the environment and with the process operators.
It has therefore appeared very desirable to discover processes which exclude the formation of nitrosoamines in order to use them in place of processes which destroy the already formed nitrosoamines, and the research of the applicant has developed in this direction.
This research has been successful, and the present invention relates to a novel purification process for obtaining DINITRO-PCBT practically free from nitrosating agents, to which said research has led. As will be apparent hereinafter, using the DINITRO-PCBT obtained by this process it is possible to prepare technical TRIFLURALIN with an NDPA content which is always less than 1 ppm. Thus the stated object is completely attained.